Temp Gauge Problem 99 Sonoma 4.3

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#1
Hi all,
My 1999 Sonoma 4.3 automatic with 203,000 miles has a temperature gauge problem. At least I think its a gauge problem.

Gauge goes to normal operating temp ( halfway)
and then after a few minutes it pegs to the right and the check gauges light comes on. Then it goes back to the halfway point and the light goes off, then it goes to three quarters, then to halfway point. All within a few minutes.

Radiator replacement 2008
Thermostat replacement 2010
full coolant level, coolant is clean, no leaks, no blowing out the tailpipe, no mixing with the oil. no bubbling from the overflow tank either.

recently replaced the smog pump and check valves, but i doubt this has anything to do with it.

Any advice is appreciated.
Thank you.
 

billr

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#2
Please clarify: Is there really a "check gauges light", or are you referring to the "check engine light" (CEL)? I am unfamiliar with that particular vehicle, but make sure of what the Owner's Manual for it calls the light you are seeing. Does it repeat the gauge and light cycle you described over-and-over, or at least periodically, or does it only do it once each time the engine is started? It might help to get it checked for any trouble codes, you can usually get that done for free at parts-supply stores.
 
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#3
Hello and thank you for the reply.
Yes, it does have a both a check gauges light and a check engine light, but thankfully, the check engine light is not on.
The gauge and light cycle repeats periodically. Except for today, when it did it after 10 minutes of running, and again after letting it sit for approx. 45 minutes.
No trouble codes in the system, however recently had a p1416 air system bank 2 code, which necessitated changing the electric smog pump, as well as the check valves. But I doubt that has any thing to do with it, at least i hope not.

Thermopstat was rplaced in Oct of 2010, due to the same cycling of gauge and light. No problems since. Until today.

When the gauge and light cycle does happen, the heat is sometimes blowing cool, sometimes, blowing warm and sometimes blows its normal hot.

Thank you in advcance for the reply.
 

billr

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#4
OK, I wanted to get those clarified and out of the way. Now it's time for one of the electrical gurus to chime in. Do you have an electrical multi-meter and know how to follow a schematic?
 

brcidd

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#5
Gage may be okay-- you say the heater temp changes as well-- then there is a coolant flow problem or a head gasket issue. Are you losing any coolant? The sending unit is probably reading steam and coolant both- registers hotter with the steam.

Have your system pressure checked, and check for exhaust bubbles emitting from radiator.
 
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#7
Not losing any coolant. No coolant mixing with oil. No white smoke from the tailpipe.

However, prior to the changing of the thermostat I was hearing some gurgling from the heater core upon initial startup and for about 5-8 minutes driving. Also, did hear some gurgling when shutting the truck off, but since thermostat was replaced, never heard the gurgling again.
 

nickb2

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#8
Thermopstat was rplaced in Oct of 2010, due to the same cycling of gauge and light. No problems since. Until today.

When the gauge and light cycle does happen, the heat is sometimes blowing cool, sometimes, blowing warm and sometimes blows its normal hot.
Sure sounds like air in the coolant system. You want to get that bled pronto. Try running the engine at 2000rpm with truck parked nose high and rad cap open. If you have access to a coolant filler funnel, great, or you can make one with an old rad cap and empty gallon jug. I would also suggest replacing the rad cap. It may be not sealing correctly, allowing air to seep in on cool down. Also check level, check if coolant is not leaking in the cab from the heater core. Is there a cooked sugar smell sometimes when driving?
 

billr

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#9
Also, try squeezing the coolant hose that feeds the water pump, probably the lower one. If you can squeeze it much (anywhere), the spring inside it might have rusted away after all these years and it may be collapsing at times and blocking flow. Not too likely, with cooling system pressure being about 15 psi over-all, but they put those springs in there for some reason...
 
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#11
My 04 Cavalier has a "check gauges light", comes on particularly if the fuel gauge registers less than 3 gallons left. also if the check engine light comes on. Assume it will go on if the temperature gauge pegs, but never that that problem, yet. Its located on the far left of the instrument panel and is a rather dim red light, hardly noticeable in the daylight. Where the gauges are large and the CEL is a very bright yellow. So got me to thinking, why is it even there?

Temperature gauges are slow responding, coolant just cannot heat or cool that quick, so when that happens, first question I ask, is that gauge sharing the ETC or does it have its own sensor, can find both. An exception to this is an exhaust temperature gauge in an air cooled aircraft engine, responds very quickly. Have to watch that baby when descending from altitude, fuel really leans out and that gauge climbs rapidly that can burn out the engine, then you will descend a lot faster than you want to.

Discouraging is to find a very clean connection on the temperature sender, means spending bucks and draining the cooling system to change it.

Another advantage of building my home high besides keeping the neighbors water out, have a fairly steep driveway, if I drive a vehicle up on car ramps facing the gauge, puts the radiator cap at the highest point so don't get air pockets when filling with coolant. But you can also buy pumps for this.

Test drove a new Focus last night, hood slopes so much, can't even see it as tall as I am, don't know if I like that, could hit the back of my garage without knowing. Know filling the radiator would be troublesome. Another thing I didn't like the head rest, not adjustable pushed my head so far forward was looking at the floor. Salesman said Ford was doing that for safety, just replied, doesn't seem very safe to me, if I am looking at the floor instead of where I am going.
 
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#12
Thanks for all the replies.....
just to clarify, no, I don't smell a burnt sugar smell when driving...and there's no coolant leaking in the cab.

HOWEVER......a few things I did notice.....
1) when I pulled over yesterday since the check gauges light was on, I noticed that the overflow had coolant up to the "full hot" line.
2) once I got home and let the engine cool down, I added approx a 1/4 of the gallon of antifreeze to the radiator, as i could not see any coolant in it. and as i added the antifreeze, there was some bubbling through the fins in the radiator.

Radiator cap is new (when radiaotor was replaced, 2008)

If it means anything, I park it on a slight decline in my driveway.

Is there a bleeder valve on this engine, and if not should I try to fit it with one?

The is a threaded squarish plug below the thermostat housing, that would seem to be a good place for a bleeder valve, no???

Thanks in advance again.
 

nickb2

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#13
once I got home and let the engine cool down, I added approx a 1/4 of the gallon of antifreeze to the radiator, as i could not see any coolant in it. and as i added the antifreeze, there was some bubbling through the fins in the radiator.
Again, I think it is air in the system seeping in by way of what you saw bubbling on radiator fins. Just cuz it's new don't mean a rock hit it or the company made 100% fully functional rads. Might have fallen on a bad rad. Try to pressure test it. Ain't no bubbles suppoesed to come out by way of rad fins or anywhere else for that matter. Get 13-15lbs pressure on the rad with a pump type tester. Maybe a tool loaner place has one handy to lend out for a small fee. On your rad cap, you should see something like 15lbs for this type of truck. You can pressure test two pounds past the cap rating safely, not more cuz some other components may burst if old and weak.
 

billr

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#14
Pressure-testing is certainly appropriate, but are you (Biagio) talking about bubbling on the outside of the radiator, or bubbles coming out of the flat tubes inside the radiator end-tank?
 
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#15
billr said:
Pressure-testing is certainly appropriate, but are you (Biagio) talking about bubbling on the outside of the radiator, or bubbles coming out of the flat tubes inside the radiator end-tank?
Yes, I am talking about the flat tubes on the inside of the radiator. Truck and radiator were cold as I was pouring in the coolant.

Also, is it normal to have what I believe to be a threaded pipe nipple below the thermostat housing? Shouldn't there be some type of bleeder valve apparatus to make bleeding air out of the system easier? Perhaps this was changed at some point... I don't know. It doesn't look factory to me.

Thank you again.